Step 1: Thing You Will Need:

Step 2: Spot Welding:

Glue 1.2 volts small batteries together so that they can be connected in parallel to each other.Now each 1.2 volt battery is rated 2400mah.Now take a Nickel strip and spot weld their positives together and then there negative together.

Now you will have it as a 1.2v 4800mah battery since they are connected in parallel.

The parallel connected batteries from the laptop should already be spot welded.Now glue both the sets together such that the negative side of 1.2 volt battery should be next to the positive side of the laptop battery.Now series connect the two batteries by doing spot welding for the final time as shown in the last picture of this step.

Step 3: Connections:

Take off the end cover of the male female USB ports.You will find four wires in it.The Black And The Red wires are only of use.Cut off the rest of them.The red wire is the positive one and the black wire is the negative.Connect the two ports in parallel as shown in the picture and increase their lengths by joining additional wires.

Make rectangular holes in the box with a razor such that the USB ports fit in them perfectly.Place the USB ports in the holes and hot glue them with a silicone gun.Now glue the batteries in the box.

Since the batteries were connected in series, they will together make up a voltage of 4.9 volts.The voltage range for charging mobile phone is 4.5 volts to 5.1 volts.

Now join the negative terminal of the battery to the negative (black) terminal of the USB ports and positive terminal of the battery to the positive(red) terminal of the USB ports.Don't forget to insulate the wires with a tape.

Step 4: Test It:

you are done!

Connect your mobile phone to the power bank with a data cable.It should start charging.

Now, to charge power bank itself, you will need a male - female cable.Connect the female side of the cable to the male port on the power bank and connect the male side of the cable to the charger.It will start charging.

I don't like to be negative towards small electronics projects like this, but this one is downright dangerous. There are a two big rules of batteries that are broken here. One, never mix different types of batteries. I realize that you're doing so to get the correct voltage, but there are some major problems that can arise from it. Two, don't different capacity batteries in series. Doing so can result in the smaller battery actually developing a negative charge, which, needless to say, it very bad. Additionally, there is no undervoltage protection on the lithium ion batteries, so they could potentially drop below a safe voltage, and possibly explode. Finally, the voltage range is far too large for safe USB use. The NiMh batteries are up to 1.8v charged and down to 0.8v empty, and the li-ion ones are 4.2v and 3.0v. That means that the whole thing is between 3.8v and 6.0v. Going under 5v won't be too bad, the phone just won't charge, but going over 5.15v can be damaging to the device. Putting 6v into it could potentially burn out the device. So, while this is a somewhat creative approach, there is a reason this isn't done.

This project works gr8 and will work for you as well.. Your theoretical points are correct but they contain too many iffs.1) When connecting is series voltage doesn't matter but amperes.The mah value of the 2 different batteries is identical.2)since u are talking about max voltage of 6V that is dangerous.I agree if only the batteries actually reach 6V.The charger we would be using to charge the powerbank itself is a 5.1V charger and i have never seen a 5.1V charger charge a battery to 6V.3) The phone still charges at a slower rate at 4.5V and that charging rate increases as it increases to 6.So automatic cut-off low voltage protection and high voltage protection.Thanks for the comment.

1) While voltage itself, as you said, is not terribly important, it's generally a given that the voltages of the batteries in series will be the same as they should be the same type of battery. As I said before, mixing battery types in the same pack is never a good idea and should be avoided.

2) If you are using a charger with a voltage of 5.1v then you're right, it will never get to a dangerous voltage. However, that means it is a constant voltage charger, which NiMh batteries are fine with, but Li-ion are definitely not. They need constant current and constant voltage chargers, very specialized, or there is a good potential for them to explode.

3) Again the issue of mixing battery types here causes problems. Even if it never drops below 4.5v for the whole pack, it is very possible for the NiMh batteries to drain completely while leaving the Li-ion partially charged. Worst case scenario, negative voltages can form across the NiMh batteries, ruining and shorting them internally, causing the Li-ion to take the full 5.1v on the next charge. causing it to potentially explode.

Again, creative approach and would be great in emergencies, but this really is too dangerous to use regularly. I mean, if you want to make it and use it, be my guest, I just want to make sure you understand the dangers and risks, and I want others to understand them as well.

I agree with Josh, this project shouldn't be used as is. Furthermore, charging different battery types with 1 charger is a bad idea: lithium cells need a very specific charging scheme, which is impossible to attain when they are connected in series with an other type of battery. As such, you can not guarantee that the lithium cells will not be overcharged. Also, there is no undervoltage protection, which could result in serious damage to the batteries. Although it's a creative idea, it's simply too dangerous and should not be attempted by anyone else.